What do bullies, bears and boxers have in common?

From time to time, they all engage in acts of aggression.

That’s easy enough to understand. But what may not be readily apparent is that they all get a neurochemical kick out of their aggressive behavior.

Researchers at Vanderbilt University have found violent or aggressive behavior may even be addictive in some of the same ways that drugs, alcohol and sex are. They all stimulate the brain to produce dopamine [DOPE-uh-mean], a chemical that produces feelings of pleasure.

In an evolutionary sense, aggression can be useful. It gives animals an advantage in gaining access to food, territory or mates, and it can help them fend off would-be predators. In human society, though, too much aggression can present all manner of problems that end up on the six o’clock news.

The researchers tested their theory by establishing a home territory for a caged mouse, with rival mice in an adjacent cage. The home mouse was trained to poke a trigger with its nose and a rival mouse would be introduced into its cage, where it was met with aggressive postures, boxing and biting.

Interestingly, the home mouse pressed the trigger on a routine basis, a sign it experienced the encounter with the intruder as a reward. But when it was given a drug that counteracts the effect of dopamine in the brain, it became less interested fighting.

The research may offer clues to understanding our society’s seeming fascination with all things violent.